Perhaps you should try some spelling variations:
thu sach » tu sach, thuat sach, thuoc sach
hieu ve » hieu va, hieu van
ve pham » vi pham, v pham, ve phan
va dinh » van dinh, va kinh, va tinh
dinh vi » dinh ve, dinh viet, dinh tri
cua tre » cuu tre, cua triet, dua tren
y nang » ky nang, ly nang, v nang
cua te » cua tu
x hoi » xa hoi, x ho, 5 hoi
o hoi » co hoi, o hoc, o hai

You may be able to get more results by adjusting your search query.

• If you are trying to use Boolean operators, they must be ALL CAPS: thu sach y nang ((x hoi) OR (o hoi)). hieu ve pham duc va dinh vi ((cua tre) OR (cua te))~.
• The words AND, OR and NOT may confuse the search; try adding quotes: "thu sach y nang ((x hoi) or (o hoi)). hieu ve pham duc va dinh vi ((cua tre) OR (cua te))~".
• Adding a wildcard symbol may retrieve word variants: thu sach y nang ((x hoi) or (o hoi)). hieu ve pham duc va dinh vi ((cua tre) OR (cua te))*.